1. Field of the Invention
The present invention relates generally to seals for oilfield applications. More specifically the present invention describes the use of hydrogel in seals for downhole use.
2. Description of the Prior Art
Seals, including o-rings, packer elements, Chevron seals, gaskets, etc., are widely used for numerous downhole oilfield applications. One ongoing issue in this area is how to energize seals and maintain sealing forces throughout seal service life. Capital loss or remediation associated with seal failure can be tremendous in certain operation areas.
One conventional method to energize seal is to utilize mechanical force to deform seal between sealing surfaces. For seals with large cross-section and/or large sealing gaps, satisfactory sealing performance is hard to achieve due to limited mechanical force. The other major problem encountered during operation is the relaxation of contact force between the seal and the sealing surfaces. This is caused primarily by the viscoelastic nature of polymeric materials used in conventional seals.
Another technique for improving seals involves the use of a pressure activated sealant that is specifically designed to seal leaks in wells and severe-environment hydraulic systems. The sealant functions by causing a pressure drop through a leak site, which in turn causes the sealant fluid to polymerize into a flexible solid seal. However, the major drawback of this technique is it requires a service engineer and a special tool to deliver the sealant to the leak site and complete the job. At that time, a significant amount of damage may have already occurred. Another disadvantage is that often tools which are installed 20,000 ft deep in the well where it is difficult and inefficient to deliver the sealant to the exact location where the leak occurs. Yet another drawback of this technique is that the sealant only starts to polymerize after a leak occurs. In certain cases, where the leakage is catastrophic, operation can fail before the polymerization process is completed.
Hydrogel technology has been rapidly developed in medical industry due to its unique response to environmental changes such as pH value, salinity, electrical current, temperature and antigens. Hydrogel is a flexible, rubber-like and solvent-swollen polymer. In an aqueous environment, hydrogel can undergo a reversible phase transformation that results in dramatic volumetric swelling and shrinking upon exposure and removal of a stimulus. A property common to all gels is their unique ability to undergo abrupt changes in volume. Gel can swell or shrink as much as 1000 times in response to small external condition changes. Through the conversion of chemical or electrical energy into mechanical work, a number of device have already been constructed which can produce forces up to 100 N/cm2 and contraction rate on the order of a second. Using microscale hydrogel, the volumetric transition can occur within minutes or even seconds. The favorable scaling of hydrogel dynamic has been the essential element in the development of micro-fluidic devices that employ hydrogel valves for flow control. One major benefit of these devices is that they are completely autonomous and therefore require no external power source.